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| == Formatting == | | == Formatting == |
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| === Line Length ===
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| There is no fixed line length. In general, strive for clarity and readability and use your own judgement.
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|
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| Everyone has access to monitors with more than 80 columns, but even so, exceptionally long lines can be hard to read. However, keeping code together on a line that is logically one unit does improve readability.
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| === Indentation === | | === Indentation === |
|
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| * Use only spaces, with 2 spaces per indent.
| | Use only spaces, and indent 2 spaces at a time. |
| * Tabs are prohibited.
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|
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| ==== Functions, class, struct, enum ====
| | We use spaces for indentation. Absolutely do not use tabs in your code. |
| | You should probably set your editor to emit spaces when you hit the tab key. |
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| The curly braces defining the beginning and end of the block should appear on their own line.
| | === Line Length === |
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| The braces should not be indented, i.e., they align at the same indentation level as the keyword such as {{codeline|class}}.
| | Keep the length of source lines to 79 characters or less, for maximum |
| | readability in the widest range of environments. This is inherited from |
| | the [https://www.gnu.org/prep/standards/standards.html#Formatting GNU Coding Standards]. |
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| The body of the block is indented.
| | === Namespace === |
|
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| Note that class access specifiers {{codeline|public}}, {{codeline|protected}}, {{codeline|private}} are not indented.
| | All code should be in the octave namespace. This is an ongoing project. We |
| | are still moving existing classes into namespaces but all new classes |
| | should go somewhere into the "octave" namespace. There is 1 extra level for namespaces |
| | inside octave to be used with care, we don't want too many namespaces. |
| | Ask before creating a new namespace. |
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|
| Example:
| | * Indent namespaces as any other block. Emacs and other editors can do this automatically. |
| | * Define namespace on the .cc files; |
| | * Do not use "using X" directives; |
| | * Do not declare anything on the std namespace; |
|
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|
| <syntaxhighlight lang="cpp"> | | {{Code|namespace style on a .h file|<pre> |
| class MatrixType
| | // Note indentation |
| | namespace octave |
| { | | { |
| public:
| | namespace math |
| enum matrix_type | |
| {
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| Unknown = 0,
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| Full,
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| Rectangular
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| };
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| | |
| }
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| </syntaxhighlight>
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| | |
| ==== Control structures (if, while, ...) ====
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| When indenting, indent the statement after control structures (like {{codeline|if}}, {{codeline|while}}, etc.).
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| If there is a compound statement, indent ''both'' the curly braces and the body of the statement (so that the body gets indented by ''two'' indents).
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| Example:
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| <syntaxhighlight lang="cpp">
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| if (have_args)
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| { | | { |
| idx.push_back (first_args); | | class foo |
| have_args = false;
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| }
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| else
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| idx.push_back (make_value_list (args, arg_nm, tmp));
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| </syntaxhighlight>
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| If you have nested {{codeline|if}} statements, use extra braces for extra clarification.
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| | |
| ==== Switch statements ====
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| Indent ''both'' the curly braces and the body of the switch statement (so that the body gets indented by ''two'' indents).
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| However, the {{codeline|case}} statement is not doubly indented and instead aligns with the first brace.
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| | |
| <syntaxhighlight lang="cpp">
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| switch (info)
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| {
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| case -1:
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| { | | { |
| cout << "function failed\n";
| | public: |
| return false; | | foo (...); |
| } | | }; |
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| case 0:
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| return true;
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| } | | } |
| </syntaxhighlight>
| | } |
| | | </pre>}} |
| ==== #ifdef directives ====
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| Indent code that follows a conditional processor directive such as {{codeline|#ifdef}} or {{codeline|#else}}.
| |
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| Example
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| <syntaxhighlight lang="cpp">
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| #if defined (HAVE_CONFIG_H)
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| # include "config.h"
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| #endif
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| </syntaxhighlight>
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| The '#' character may also be placed with the directive rather than remaining in column 1 if this looks better.
| |
| | |
| ==== Split long expressions ====
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| Split long expressions in such a way that a continuation line starts
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| with an operator rather than identifier. If the split occurs inside
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| braces, continuation should be aligned with the first char after the
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| innermost braces enclosing the split. Example:
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| | |
| <syntaxhighlight lang="cpp">
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| SVD::type type = ((nargout == 0 || nargout == 1)
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| ? SVD::sigma_only
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| : (nargin == 2) ? SVD::economy : SVD::std);
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| </syntaxhighlight> | |
| | |
| ==== Optional braces ====
| |
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| Consider putting extra braces around a multi-line expression to make it
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| more readable, even if they are not necessary. Also, do not hesitate to
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| put extra braces anywhere if it improves clarity.
| |
| | |
| === Pointer and Reference appearance ===
| |
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| Declarations of pointers have the '*' character cuddled with the ''name'' of the variable.
| |
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| <syntaxhighlight lang="cpp">
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| unsigned int *pointer_variable;
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| </syntaxhighlight>
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| However, references have the '&' character cuddled with the ''type'' of the variable.
| |
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| <syntaxhighlight lang="cpp">
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| unsigned int& reference_variable;
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| </syntaxhighlight>
| |
| | |
| === Miscellaneous ===
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| The negation operator is written with a space between the operator
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| and its target, e.g., {{codeline|! A}}.
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| | |
| === Function headers ===
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| In general, in non-header files, format function headers like this:
| |
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| <syntaxhighlight lang="cpp">
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| static bool
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| matches_patterns (const string_vector& patterns, int pat_idx,
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| int num_pat, const std::string& name)
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| </syntaxhighlight>
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| The return type of the function and any modifiers are specified on the first
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| line. The function name on the second line should start in column 1, and
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| multi-line argument lists should be aligned on the first character after the open
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| parenthesis. Put a space before the left open parenthesis and after
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| commas, for both function definitions and function calls.
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| For header files, or in class definitions, it may look better not to split the return type from the rest of the function header. Use your own judgement.
| |
| | |
| === Class declarations ===
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| The access specifier ({{codeline|public}}, {{codeline|protected}}, {{codeline|private}}) should always be stated rather than relying on the C++ language defaults for a particular object (for example, "{{codeline|class}}" = "{{codeline|private}}").
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| Within a class, the different access blocks should appear in the order 1) {{codeline|public}}, 2) {{codeline|protected}}, 3) {{codeline|private}}.
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| Within an access block, member functions (methods) should be specified before member variables. If there are both member functions and member variables use
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| //--------
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| between the sections to visually separate the two categories.
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| === Namespace ===
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| All code should be in the {{codeline|octave}} namespace or in a namespace below it.
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| Namespaces should start and stop using the special macros {{codeline|OCTAVE_BEGIN_NAMESPACE(XXX)}} and {{codeline|OCTAVE_END_NAMESPACE(XXX)}}. There is no indentation of code that is placed into namespaces using these macros.
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| Example
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| {{Code|Use of namespace macros|<syntaxhighlight lang="cpp">
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| OCTAVE_BEGIN_NAMESPACE(octave)
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| OCTAVE_BEGIN_NAMESPACE(math)
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| template <typename T>
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| void
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| umfpack_report_control (const double *Control);
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| OCTAVE_END_NAMESPACE(math)
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| OCTAVE_END_NAMESPACE(octave)
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| </syntaxhighlight>}}
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| If bare namespace directives must be used, as occasionally is required in Qt code, then the code within the namespace should be indented.
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|
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| {{Code|bare namespace usage|<syntaxhighlight lang="cpp"> | | {{Code|namespace style on a .cc file|<pre> |
| // Note indentation and that functions are not defined as "octave::math::foo:foo" | | // Note indentation and that functions are not defined |
| | // as "octave::math::foo:foo" |
| namespace octave | | namespace octave |
| { | | { |
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| } | | } |
| } | | } |
| </syntaxhighlight>}} | | </pre>}} |
| | |
| ==== Other Guidelines ====
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| * Do not use {{codeline|using XXX;}} directives
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| * Do not declare anything on the {{codeline|std::}} namespace
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| == Naming ==
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| Use lowercase names if possible. Uppercase is acceptable for variable names consisting of 1-2 letters. Do not use mixed case (a.k.a. CamelCase) names.
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| === Member Variables ===
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| Member variables should use the prefix "m_" whenever possible.
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| === Class Variables ===
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| Class variables should use the prefix "s_" (for "static") whenever possible.
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| === Filenames ===
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| As with m-files, the file name of a C++ source file containing a class should match the name of the class defined within the file. For example, "password.h" defines the class "password" rather than "passwd.h" which is a common abbreviation for "password".
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| == Header Files == | | == Header Files == |
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| Header files should not use any "#if defined (HAVE_FEATURE)" conditionals. This is not quite true yet, but we are almost there. '''No new conditionals may be added.''' | | Header files should not use any "#if defined (HAVE_FEATURE)" conditionals. This is not quite true yet, but we are almost there. '''No new conditionals may be added.''' |
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| == C++ features == | | == Other C++ features == |
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| === references === | | === C++11 === |
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| Use references when passing variables that will be changed by a subroutine rather than the C-style method of passing pointers.
| | C++11 features are generally allowed. Check if the feature you want to |
| | use has been already used. If not, ask on the mailing list. |
|
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|
| {| class="wikitable"
| | ==== auto ==== |
| ! style="color:green;" | good
| |
| ! style="color:darkred;" | bad
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| |-
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| | <syntaxhighlight lang="c++">
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| void foo (int& a_ref)
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| {
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| // foo changes content of `a_ref`
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| a_ref = a_ref + 1;
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| }
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| void bar ()
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| {
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| int a = 42;
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| foo (a);
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| }
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| </syntaxhighlight>
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| | <syntaxhighlight lang="c++">
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| void foo (int *a_ptr)
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| {
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| // foo changes content of `a_ptr`
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| *a_ptr = *aptr + 1;
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| }
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| void bar ()
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| {
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| int a = 42;
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| foo (&a);
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| }
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| </syntaxhighlight>
| |
| |}
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| When passing variables that are large, but will not be changed in a subroutine (read-only), use {{codeline|const}} references. This helps avoid overflowing the finite stack capacity of a program while still ensuring that read-only access is enforced.
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| {| class="wikitable"
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| ! style="color:green;" | good
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| ! style="color:darkred;" | bad
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| |-
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| | <syntaxhighlight lang="c++">
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| void foo (const std::string& str_ref)
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| {
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| // foo does not change content of `str_ref`
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| }
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| void bar ()
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| {
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| std::string str ("This is a large variable, however as a reference it will take up just 8 bytes on the stack when passed to the subroutine foo()");
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| foo (str);
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| }
| |
| </syntaxhighlight>
| |
| | <syntaxhighlight lang="c++">
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| void foo (std::string str_copy)
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| {
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| // foo does not change content of `str_copy`
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| }
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| void bar ()
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| {
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| std::string str ("This is a large variable that will be copied on to the stack and passed as a temporary variable to the subroutine foo()");
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| foo (str);
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| }
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| </syntaxhighlight>
| |
| |}
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| === new/delete ===
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| Pointers that will be allocated memory with {{codeline|new}} should be initialized with the C++ literal {{codeline|nullptr}}, not the numerical value 0 or the macro {{codeline|NULL}}.
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| The {{codeline|delete}} keyword accepts {{codeline|nullptr}} and programmers should not put an {{codeline|if (ptr)}} guard around {{codeline|delete}}.
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| {| class="wikitable"
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| ! style="color:green;" | good
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| ! style="color:darkred;" | bad
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| |-
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| | <syntaxhighlight lang="c++">
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| delete ptr;
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| </syntaxhighlight>
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| | <syntaxhighlight lang="c++">
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| if (ptr)
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| delete ptr;
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| </syntaxhighlight>
| |
| |}
| |
| | |
| === lambda expressions ===
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| When capturing variables from the surrounding function, explicitly list the variables being captured rather than relying on a default capture by value (`[=]`) or by reference (`[&]`). This more clearly captures the programmer's intent and makes the code more understandable.
| |
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| === std::string ===
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| When an empty string is required, use <code>""</code>, rather than creating an empty
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| string object with <code>std::string ()</code>.
| |
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| === auto ===
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|
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| Use of {{codeline|auto}} is allowed only where it helps readability | | Use of {{codeline|auto}} is allowed only where it helps readability |
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| * Beware of copy when using {{codeline|auto}} in for loops. Pass by reference and use {{codeline|const}} unless you're dealing with simple types such as {{codeline|int}}. See [http://lists.gnu.org/archive/html/octave-maintainers/2016-06/msg00144.html 'auto' uses and for-range loops] on the maintainers mailing list for more details. | | * Beware of copy when using {{codeline|auto}} in for loops. Pass by reference and use {{codeline|const}} unless you're dealing with simple types such as {{codeline|int}}. See [http://lists.gnu.org/archive/html/octave-maintainers/2016-06/msg00144.html 'auto' uses and for-range loops] on the maintainers mailing list for more details. |
|
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|
| === C++ style casting ===
| | === C++14 === |
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| Always use one of the four C++ long style casting forms ({{codeline|static_cast}}, {{codeline|dynamic_cast}}, {{codeline|reinterpret_cast}}, {{codeline|const_cast}}) rather than C-style forms (type cast {{codeline|(new_type) variable}} or the function form {{codeline|new_type (variable)}}).
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| === C++11 features ===
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| A C++11 compatible compiler is required for [[Building | building Octave]]. Please make use of all C++11 features.
| |
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| === C++14, C++17, C++20 features === | |
|
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|
| Try to avoid C++14, C++17, or C++20 features. Octave is widely used in very old systems and we want them to be able to use up to date versions of Octave. Building a recent compiler in such systems is not a trivial task so the limitation must happen
| | Do not use C++14 features. Octave is widely used in very old systems and we |
| | want them to be able to use up to date versions of Octave. Building a recent |
| | compiler in such systems is not a trivial task so the limitation must happen |
| in Octave. | | in Octave. |
|
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|
| If the implementation using a C++14, C++17, or C++20 feature is very beneficial, make it optional via <code>configure</code> feature detection or also implement an alternative code in the absence of said feature. In any case, please get in contact with the Octave maintainers on [https://octave.discourse.group/c/maintainers/7 Discourse].
| | An exception: code that requires C++14 feature must also implement an |
| | | alternative code in the absence of said feature. In such case, use a |
| <syntaxhighlight lang="cpp">
| | configure check. This increases maintenance a lot, must be used sparsely, |
| #if defined (HAVE_THIS_C14_FEATURE)
| | and requires approval from other maintainers. |
| // code that really needs it
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| #else
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| // alternative code in its absence
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| #endif
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| </syntaxhighlight>
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| | |
| == Doxygen ==
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| Doxygen documentation can be a great help when developing octave however the current state has a lot of room for improvement. For more information about Doxygen in Octave look at [[Doxygen]].
| |
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| === Doxygen Style Guide ===
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| Doxygen allows for a variety of commenting styles. In order to maintain uniformity across the entire project the following rules should be applied:
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| * For Doxygen comments use only {{codeline|//!}} and NOT {{codeline|/*! ... */}}, regardless of the size of the block comment
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| * Use {{codeline|@}} for any [https://www.stack.nl/~dimitri/doxygen/manual/commands.html Doxygen Special Commands]
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| * Use as little formatting as possible. Restrict to [https://www.stack.nl/~dimitri/doxygen/manual/markdown.html Markdown] and avoid HTML-markup.
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| * Do NOT use the {{codeline|@brief}} command, the first sentence will automatically be used as the summary description.
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| * The first sentence should describe briefly what the function does and end with a period.
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| * Leave a blank line between the Doxygen comment and function definition.
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| An example of properly used Doxygen would look like:
| |
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| <syntaxhighlight lang="cpp">
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| //! Does something interesting with its arguments.
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| //!
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| //! Long comment with **bold** special commands.
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| //!
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| //! @param some_param Really should figure out what to do.
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| //! @param another_param Does something cool with @p some_param.
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| //!
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| //! And some example using syntax highlighting:
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| //!
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| //! @code{.cc}
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| //! double v = 1.0;
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| //! int n = 2;
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| //! some_function (v, n);
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| //! @endcode
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| void
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| some_function (double some_param, int another_param)
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| {
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| // ...
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| }
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| </syntaxhighlight>
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| == Comments ==
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| === FIXME notes ===
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| The preferred comment mark for places that may need further attention is
| |
| with {{codeline|FIXME:}} comments.
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|
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|
| [[Category:Development]]
| | #if defined (HAVE_THIS_C14_FEATURE) |
| | // code that really needs it |
| | #else |
| | // alternative code in its absence |
| | #endif |